The possible association between acute respiratory failure and disseminated intravascular coagulation was examined in eight patients with severe acute respiratory failure--a condition characterized by tachypnea, right to left intrapulmonary shunting of blood greater than 30 per cent of cardiac output, increased pulmonary artery pressure with low or normal pulmonary artery wedge pressure and roentgenologic interstitial pulmonary edema. Treatment consisted of mechanical ventilation with positive end expiratory pressure sufficient to minimize intrapulmonary shunting. There was no abnormality in platelet concentration fibrin split product concentration, fibrinogen concentration, prothrombin time or activated partial thromboplastin time during the period of most severe respiratory failure in any patient. However, mean platelet concentration fell to 90,000+/-9,000 per cubic millimeter, less than 0.001, and mean fibrin split product levels rose to 60+/-10 micrograms per milliliter, p less than 0.05, the fourth day after the onset of acute respiratory failure. No significant change occurred in other coagulation parameters. Disseminated intravascular coagulation developed in none of the patients nor was there any correlation between coagulation abnormalities and severity of acute respiratory failure that would suggest a cause and effect relationship.